Make PrefService available in *ash

ash/mus/shell_delegate_mus.cc

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ash/mus/shell_delegate_mus.h"
 
 #include <utility>
 
 #include "ash/gpu_support_stub.h"
 #include "ash/mus/accessibility_delegate_mus.h"
@@ skipping 137 matching lines @@
 base::string16 ShellDelegateMus::GetProductName() const {
   NOTIMPLEMENTED();
   return base::string16();
 }
 
 gfx::Image ShellDelegateMus::GetDeprecatedAcceleratorImage() const {
   NOTIMPLEMENTED();
   return gfx::Image();
 }
 
+PrefService* ShellDelegateMus::GetActiveUserPrefService() const {
+  NOTREACHED();

[sky, 2017/04/26 19:51:57]

Please add a comment as to why the NOTREACHED as it isn't obvious from looking
at this code why it's here.

[afakhry, 2017/04/26 22:43:50]

Done.

+  return nullptr;
+}
+
 bool ShellDelegateMus::IsTouchscreenEnabledInPrefs(bool use_local_state) const {
   NOTIMPLEMENTED();
   return true;
 }
 
 void ShellDelegateMus::SetTouchscreenEnabledInPrefs(bool enabled,
                                                     bool use_local_state) {
   NOTIMPLEMENTED();
 }
 
 void ShellDelegateMus::UpdateTouchscreenStatusFromPrefs() {
   NOTIMPLEMENTED();
 }
 
 }  // namespace ash